Reciprocating air hammer

ABSTRACT

The hammer barrel is supported by a rear header and, in turn, supports a front header. A piston is reciprocated in the barrel under the control of a reversible kick valve. The piston drives a tappet and moil which are supported for reciprocation by the front header. The tappet is continually biased to full extended position by a metering cutt-off valve which is subject continually to live air and which can seat to cut off the air supply to the barrel and stop the hammer when the tappet is substantially fully extended. The metering cut-off valve controls the rate of flow of live air so as to prevent excessively violent responses of the piston thereto. The metering cut-off valve is mounted in, and guided by, an air inlet fitting, the two providing a sub-assembly which can be installed as a unit in the rear header of the barrel. An axially free floating rigid stainless steel rod constrains the metering cut-off valve and tappet to coaxial movement together in substantially fixed axially spaced relation and unseats the metering cut-off valve when the tappet is retracted rearwardly by forcing the moil against the work. One end of the rod abuts the metering cut-off valve and the other end abuts the tappet, but the rod is not fixedly attached to either. The rod is supported for axial reciprocation by a bore in the piston and by a fixed rear bushing in the barrel. A valve spool on the tappet closes a vent when the tappet is extended and opens the vent when the tappet is retracted, thereby controlling venting of the barrel bore.

United States Patent 1 Gunning RECIPROCATING AIR HAMMER [75] Inventor: Samuel D. Gunning, Cleveland, Ohio [73] Assignee: Kent Air Tool Co., Kent, Ohio [22] Filed: Aug. 11, 1971 21 Appl. No.: 170,810

Primary Examiner-Ernest R. Purser Attorney-John Harrow Leonard [57] ABSTRACT The hammer barrel is supported by a rear header and, in turn, supports a front header. A piston is reciprocated in the barrel under the control of a reversible kick valve. The piston drives a tappet and moil which June 19, 1973 are supported for reciprocation by the front header. The tappet is continually biased to full extended position by a metering cutt-off valve which is subject continually to live air and which can seat to cut off the air supply to the barrel and stop the hammer when the tappet is substantially fully extended. The metering cut-off valve controls the rate of flow of live air so as to prevent excessively violent responses of the piston thereto. The metering cut-off valve is mounted in, and guided by, an air inlet fitting, the two providing a sub-assembly which can be installed as a unit in the rear header of the barrel. An axially free floating rigid stainless steel rod constrains the metering cut-off valve and tappet to coaxial movement together in substantially fixed axially spaced relation and unseats the metering cut-off valve when the tappet is retracted rearwardly by forcing the moil against the work. One end of the rod abuts the metering cut-off valve and the other end abuts the tappet, but the rod is not fixedly attached to either. The rod is supported for axial reciprocation by a bore in the piston and by a fixed rear bushing in the barrel. A valve spool on the tappet closes a vent when the tappet is extended and opens the vent when the tappet is retracted, thereby controlling venting of the barrel bore.

12 Claims, 5 Drawing Figures PMENTEB JUN 1 W5 SHEEIIUFZ mi INVENTOR.

SAMUEL D. GUNNING w N Q N Q um Am H H l D n H Qufl /4 D m PAIENIED mm 9 ma 739 ,352

sum 2 0F 2 INVENTO SAMUEL D. GUNNIILNG ATTORNEY.

1 RECIPROCATING AIR HAMMER CROSS REFERENCE TO RELATED APPLICATION This invention is directed to improvements on the air hammer disclosed in my copending application, Ser. No. 10,826, filed Feb. 12, 1970 now US. Pat. No. 3,625,295, issued Dec. 7, 1971 and entitled Air Hammer.

BACKGROUND OF INVENTION 1. Field of Invention Air hammers with axially reciprocating tools.

2. Description of Prior Art The above identified patent discloses an air hammer wherein the moil is continually biased to fully extended position by live air, and wherein movement of the moil from a fully extended position to a retracted position initiates operation of the hammer which then continues to operate uninterruptedly until such time, as the moil is again permitted to move to a fully extended position, as by withdrawing the moil from the work. The hammer has a piston which delivers repeated blows to a tappet which transfers the resultant impacts to the moil. The reciprocation of the piston, once its operation is initiated by retraction of the moil, is controlled by a reversing kick valve.

SUMMARY OF INVENTION The present invention incorporates the above described features and structure of my copending application and certain improvements. The improvements reside in the inclusion of a metering cut-off valve; an inlet fitting and metering cut-off plug combined in a sub-assembly, which can be installed readily as a unit in the hammer; the specific connection between the valve plug and tappet so as to bias the tappet, and thereby the moil, to extended position while reducing inertial stresses; and the manner of venting of the barrel bore at the end of the piston stroke by the valving spool reciprocable with the tappet.

Various other specific objects and advantages will become apparent from the following description wherein reference is made to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of a hammer embodying the principles of the present invention;

FIG. 2 is a longitudinal sectional view of the hammer and is taken on the line 2-2 in FIG. 1;

FIG. 3 is a fragmentary cross sectional view taken on the line 3-3 in FIG. 2;

FIG. 4 is a fragmentary cross sectional view taken on the line 4-4 in FIG. 2; and

FIG. 5 is a diagrammatic longitudinal sectional view, similar to FIG. 2, showing various bores and ducts, parts, and valving of the hammer by which operation and control are effected.

PREFERRED EMBODIMENT OF THE INVENTION Referring to the drawings, the air hammer comprises a cylinder barrel 1 supported by a rear inlet header 2 and supporting a moil and tappet supporting front header 3. The header 3 is made of two block portions or parts 3a and 3b secured in fixed position by a clamping portion 30. The headers 2 and 3 and the barrel 1 are clamped in assembled relation to each other by bolts 4.

The barrel 1 has a power cylinder bore 5. The rear header 2 has an axial passage 6 in which an inlet fitting 7 is mounted for supplying live air to the bore 5. A block 8, composed of two parts 8a and 8b, is mounted in the rear end of the bore 5. The part 8a has a bore 9 which is in communication at its outer end with the interior of the fitting 7 and which at its inner end is in communication with a coaxial bore 10 of smaller diameter than the bore 9. The bore 10, in turn, is in communication at its inner end with a kick valve bore 11 in which an annular kick, or rapid reversing, valve plug 12 is mounted for axial reciprocation, as is described fully hereinafter.

Mounted for axial reciprocation in a suitable bore in the header 3 is a moil or tool 13. The header 3 has a guide bore 14 and an auxiliary valving bore 15. The bore 15 at its forward end has an exhaust passage 16 and at its rear endhas an exhaust duct 17.

The moil 13 is driven by a tappet 18 which may be integral with, or separate from the moil 13. The tappet 18 comprises a stern 18a and an integral valving spool 18b of larger diameter than stem 18a. The inner end of the stem 18a extends into the forward end of the bore 5 for receiving the blow of a power piston while the tappet 18 is retracted. The valving spool 18b is reciprocable in the auxiliary valving bore 15.

The stem 18a is provided with passage means which provide communication between the forward end of the bore 5 and the auxiliary valving bore 15 behind the spool 18b when the tappet 18 is moved to, or very close to, fully extended position. In the extended position of the tappet 18, the portion of the auxiliary bore 15 behind the spool 18b is vented to atmosphere through the exhaust duct 17 and the outlet passage 16 is closed by the spool 18b.

In the form illustrated, these passage means are provided by flutes or flats 19 on the exterior of the stem 18a. The flats 19 extend from the inner end of the stem 18a partway toward the spool 18b so that their outlet ends are exposed within the bore 15 when the tappet 18 is fully extended. The exhaust passage 16 vents the bore 15 at the front of the spool 18b until the tappet 18 is substantially fully extended.

The venting through the exhaust duct 17 has the dual advantage of admitting outside air behind the spool 18b during its initial movement on its power stroke, thus relieving any hold back effects of reduced atmospheric pressure, but principally permitting bleeding of any residual live air from the forward end of the bore 5 while the tappet l8 and moil 13 are in extended position.

For driving the moil 13, a power piston 20 is mounted for reciprocation in the bore 5 from a retracted position, in which it is at the rear end of the bore 5 in FIG. 2, to an extended position in which it is at the front of the bore 5.

Live air is admitted to the rear end of the bore 5 for driving the piston on its power stroke and is admitted to the front end of the bore 5 for driving the piston on its return stroke. The live air is supplied from the inlet fitting 7 to the bore 5 through bores: 9, l0, and 11 under the control of the kick valve plug 12. For this purpose, the bore 11 has an annular port 22 which is connected by ducts 23 to a groove 24 in the bore 5 so that air can be admitted to the bore 5 at the rear end of the piston 20 when the piston 20 is spaced a short distance to the right of the inner face of the block part 8b.

In order to admit air from the valving bore If to the front end of the bore 5 when the valve plug 12 is positioned for the return stroke of the piston 20, the barrel 1 is provided with suitable ducts 26 which at their rear ends communicate with the bore 11 through lateral ducts 27 and a port-28 controlled by the valve plug 12. The ducts 26 deliver air to the bore 5 through a groove 29 disposed at the front end of the bore 5.

Upon admission of air to the ducts 26, after the piston has delivered its blow and after venting the bore 5 at the rear of the piston, as is later explained, the piston 20 is driven to the left. When the valve plug 12 is moved forwardly to close the port 22, it opens the port 28 and admits live air to the forward end of the bore 5 for driving the piston 20 on its return stroke. Upon partial return of the piston 20 live air at the front of the piston 20 is vented to atmosphere through a groove 30, a duct 31, valving bore 15 and the outlet passage 16 while the tappet 18 is out of extended position.

The kick valve plug 12 is arranged to close the port 22 and to open the port 28 when the valve plug 12 is driven fully forwardly in FIG. 2, and to open the port 22 and close the port 28 when the valve plug 12 is driven fully rearwardly.

Live air from the bore 5 is admitted by a duct 33, when open, into a valving trough 34 at the front of a flange 35 on the kick valve plug 12 and live air from the bore is admitted by a duct 36, when open, into the trough 34 to the rear of the flange 35.

These ducts and their inlets and outlets are arranged so that the kick valve plug 12 is moved to its reversing positions in relation to extended and retracted positions of the piston 20.

Thus live air is admitted into the barrel bore 5 through the fitting 7, the bores 9, 10, and 11, in order, and the repeated succession of piston blows is controlled by the kick valve plug 12.

For efficient operation of the hammer, the moil 13 must be urged to, and yieldably continually held in the fully extended position by live air from the pressure source, and the live air to the piston must be metered properly.

To cut off entirely the admission of the air to the bore 5, to bias the tappet 18 to fully extended position, to meter the air admitted to the bore 5, and to operate in response to the tappet position, a combined metering and cut-off valve 39 of the present improvement is provided.

The cut-off and metering valve 39 includes the fitting 7, which has a valve bore 40 with a larger diameter portion 40a at its inner end, and a metering cut-off plug 41. The plug 41 has a stem 42 which is reciprocable in the bore 40 and a coaxial head 43. The stem ,42 fits the bore 40 with operating clearance and is provided with flutes 42a to permit a free flow of live air from the outer end of the fitting 7 into the outer end of the bore 40a.

The head 43 is shaped and arranged to enter the bore 10 with operating clearance when the plug 41 is in its extended position.

An annular metering flange 44 is provided on the plug 41 at the rear of the head 43 and is disposed in coaxial relation to, and in radially inwardly spaced rela tion to, the wall of the bore portion 40a. The radial spacing between the flange 44 and the wall of the bore 40a is selected to provide a metering throat 45 of the proper size to meter the proper rate of flow of live air for optimum speed and acceleration of the piston.

The forward face of the flange 44 has a seating area 46 which, in the forwardmost position of the plug 41, seats on the complementary seating area 47 on the shoulder between the bores 9 and 10 and thereby shuts off completely the admission of live air to the kick valve bore 11.

In order to operate the metering cut-off valve 39 in properly timed relation to the operation of the piston 20, the valve plug 41 is drivingly connected to the tappet l8, and thereby to the moil 13, by means of a rigid rod 50. The rod 50 is not fastened fixedly to either the plug 41 or the tappet l8, butat the rear end 50a is abutted with the valve plug 41, and at the front end 50b with the rear end of the tappet 18. Those opposite ends provide abutments, the faces of which engage complementary faces on the plug 41 and tappet 18, respectively. The ends 50a and 50b are a distance apart such that with the plug 41 seated against its seat 47 in the header 3, and the tappet in fully extended position and with the end 50a of the rod abutting the head 43 of the plug 41, the end 50b is about one sixty-fourth to one thirtysecond inches short of contact with the adjacent end of the tappet stem 18a. If this clearance is too small, parts may jam or not seat properly, and if too great, causes destructive hammering of the rod to against the plug 41 and the tappet due to inertial forces.

Thus the rod 50 constrains the plug 41 and tappet 18 to move in substantially fixed relation to each other, but since the rod 50 is not fastened to the plug 41, the inertial forces, generated in the rod 50 due to its being moved at high velocity to the extended position by the plug 41, are not imposed on the plug 41 or the seat 47 when the plug 41 seats. Instead, these inertial forces are imposed on the tappet 18 and moil 13 in the work direction. Again, upon return of the rod 50, it does not generate inertial forces which are impacted on the plug 41 while it is stationary. Instead, the plug 41 and rod 50 build up speed from rest concurrently. Because of vibrational forces produced by operation of the hammer, the rod 50 is composed of stainless steel which appears to withstand the type of vibrational stress thus imposed, without fatigue and crystallization, to a higher degree than rods composed of other metals, and especially to be less sensitive to stress concentrating notches or cracks.

The rod is supported and guided for axial reciprocation by the wall of a bore 51 in the piston 20 and by a bushing 52 mounted in the barrel. The rod 50 fits with operating clearance in the bore 41 so as to permit seepage of air from one end of the piston 20 to the other, thus balancing the air pressure in the bore 5 at opposite ends of the piston 20 when the hammer is left idle for an interval. The rod fits in the bushing 52 so that no appreciable air can pass therethrough. A seat 53 for the spool 18b is provided to limit its extreme extended position.

The importance of the metering function of the plug 41 and flange 44 should be noted. The operation of air hammer pistons is exceedingly rapid. This is desirable, and to assure such operation the practice has been to admit air freely into the hammer inlet. However, it appears that this approach is erroneous, as the admission of air unrestrictedly results in too violent a response of the piston on its respective strokes. This excessive, or over, response developes extremely high dynamic inertial forces in the piston, which must be withstood initially by low dynamic or static inertial forces of the tappet 18 and moil 13, and then of the header 3 as the tappet 18 accelerates and strikes its seat 53. The resultant impact and vibrational forces are transmitted by the header 3 to the remainder of the structure.

As a result of too violent a response of the piston, the air supply, instead of being used efficiently for the intended work is used in a manner causing excessive breakage and wear of the parts of the hammer and its support and lowered efficiency.

By metering the rate of introduction of the live air, by the metering cut-off valve 39, the excessive re sponses of the piston 20 are eliminated, and the operating response is such that for a given live air source pressure and volume of air, the inertial forces are reduced to a degree and so applied that a higher proportion of useful power at the moil point is provided. Thus the energy of the moving piston 21) is proportioned more to useful work than to damaging stresses.

For example, by properly metering the rate of live air input by the metering cut-off valve 39, the total air input at a given pressure can be reduced almost 50 percent from that theretofore so applied and causing the over-response, but with a useful work output reduction of not more than percent, while concurrently freeing the hammer from excessive and dangerous over stresses, fatigue, wear, and breakage.

These advantages are augmented by the starting of the piston 20 from proper positions at all times, and by sharp cut-offs of the live air to opposite ends of the cyl inder power bore 5 at the ends of the piston strokes. It might at first glance appear that the groove 30 could be vented to the atmosphere directly without passing through the valving bore and passage 16, and that these and the valving spool 18b on the tappet 18 could be eliminated as the plug 41 itself stops the admission of air when the piston and tappet 18 approach extended position. They could be eliminated, but only at a sacrifice in quality of operation, and in starting operation after an interval of idleness. With the provision of the metering cut-off valve 39, the valving by the piston spool 18!), and the venting described, improved operation is obtained.

Due to the flats 19 on the tappet stem 18a, air in front of the piston 20 is vented to atmosphere through the duct 17 at all times while the tappet 18 is extended. Consequently, residual pressure of air at the rear of the piston, upon shut-off of the hammer, can move the piston to fully extended position in readiness for the next operation. As mentioned, the rod 50 fits the bore 51 in the piston with operating clearance so that live air and air under residual pressure can seep through the space between the rod 50 and the wall of the bore 51 and eventually equalize at opposite ends of the piston 20. Due to this seepage and the flats 19, the live air, or air under residual pressure, in the bore 5 eventually vents to the bore 15 around the tappet stem 18a and through the exhaust duct 17.

This improves starting because the pressure in the entire bore 5 is reduced to atmospheric so when the moil 13 is retracted, to start operation, the kick valve 12 be comes operative instantly to drive the piston either on its power stroke or return stroke, depending on the random location in which the kick valve happened to have stopped. Also, when retracting pressure is removed from the moil 13, the live air seats the plug 41, moving the tappet 18 forwardly so that the spool 18b is just short of the seat 53. The slight spacing of the spool 18b and seat 53 is due to the slight clearance of about one sixty-fourth of an inch between the ends of the rod 50 and the plug 41 and tappet stem 18a, heretofore described.

With the tappet 18 in partially extended position, any air under residual pressure in the bore 5 at the rear of the piston 20 will move the piston 20 to its forwardmost position and against the tappet 13 and urge the tappet toward fully extended seated position. in this condition, the hammer can be started instantly upon subsequent retraction of the tappet 18 by pushing it against the work.

Since the metering cut-off valve 39 is closed at all times while the moil 13 is out of engagement with the work, leakage of air from the bore 5 while the hammer is idle is eliminated.

The reversal of the strokes of the piston 20 by the kick valve 12, once the metering cut-off valve is unseated, is the same, generally, as disclosed in my above identified copending application. The important differences reside in the metering function of the valve 39; the specific means employed for correlating its operation with that of the piston 20 and tappet l8, and for maintaining the tappet 18 fully extended in every position into which the hammer is moved so long as the tappet is not forced against the work; the fact that the valve 39, when subjected to live air, can overcome the dead weight of the tappet and moil, even when the valve 39 is open, and move the idle moil and tappet to fully extended position so that the: hammer, after temporarily being withdrawn from the work, is instantly responsive when the moil is reapplied to the work; and the elimination of the expensive air duct for admitting live air continuously from the source to the auxiliary valving bore at the rear of the tappet spool to bias the tappet to extended positions, as in my above identified patent.

Briefly, the operation is as follows:

Starting with the moil 13 extended, the valve plug 41 is seated on the seat 47 and no live air is admitted to the bore 5. When the moil 13 is retracted by forcing it against the work, it forces the tappet 18 and rod 50 to retracted position, unseating the plug 41 and thereby opening the valve 39 to admit air at a metered rate of flow to the kick valve 12.

Depending upon the position of the valve 12, air is admitted to the proper end of the bore 5 for driving the piston 20 toward the other end of the bore 5. Assume the kick valve 12 and piston 20 arein the position illustrated in FIG. 5, air is admitted through the port 22, duct 23, and groove 24 to the rear of the piston 20, driving it on its power stroke. The bore 5 in front of the piston has been vented to atmosphere by the groove 30,

the duct 31, the auxiliary valving bore 15, and the pas-.

sage 16. As the piston is driven forwardly, it closes the groove 30 and then continues forwardly blocking the duct 33 and striking the tappet 18. As it passes the inlet of the duct 36, live air is admitted through the duct 36 to the bore 34 at the rear of the flange 35 of the kickvalve 12, and drives the kick valve 12 forwardly, closing the port 22 to live air and opening the port 28 which, through ducts 27 and 26, admits live air to the front of the bore 5 through the groove 29. Almost simultaneously it uncovers the groove 30 to exhaust live air from the rear of the bore 5. When the piston 20 moves almost to its rearmost position, it opens the inlet of the duct 33, admitting live air to the bore 34 in front of the kick valve flange 35 to reverse the valve 12 to readmit air to the rear of the bore 5, thus starting a repeat of the cycle, the front of the bore meanwhile having been vented to atmosphere.

When the tappet 18 is fully extended, the spool 18b blocks the passage 16 so that air under pressure cannot be vented from either end of the bore 5 through the groove 30 and duct 31. This stops the piston 20. The admission of live air by the metering cut-off valve 39 is stopped, also, shutting down operation.

Having thus described my invention, I claim:

1. In a reciprocating air hammer:

a moil member;

a moil driving tappet member;

a body supporting the members for reciprocation to extended and retracted positions, respectively;

a power cylinder bore coaxial with the tappet memher;

a power piston in the bore cylinder reciprocable relative to the body and to the tappet member from a retracted starting position to an extended position wherein it delivers a blow on the tappet member, and from the extended position to the starting position;

said body having a live air inlet connected with said bore;

valve means for successively alternately connecting the bore at one face of the power piston to said inlet for admitting air under pressure for driving the power piston on its power stroke, and at the opposite face of the power piston for driving the power piston on its return stroke;

characterized in that:

a metering cut-off valve is connected to the body inlet and is connectable to a source of air pressurized to a predetermined pressure, and is operative in all open positions, to meter the live air admitted to the power cylinder bore by way of the inlet and valve means, in all open positions of the metering valve, to a rate of flow substantially less than that at which the piston would operate if connected to said source for free and unrestricted flow of the pressurized air to said valve means, and for step ping the admission of air to the power cylinder bore while the valve is closed; and

means drivingly connect the valve and tappet for opening and closing the valve in fixed relation to the tappet positions.

2. The structure according to claim 1 wherein the metering valve includes a valving bore connected to said inlet, and a metering and cut-off valve plug mounted in the valving bore for reciprocation axially thereof, and defining with the valve bore wall a restrictive flow passage operative to restrict the flow through said bore in all open positions of the plug.

3. The structure according to claim 2 wherein the valve is a separate unit and further includes an inlet fitting, the valving bore is in the fitting, and said fitting,

with the valve plug installed therein, is connectable as a subassembly unit to the body.

4. The structure according to claim 3 wherein the valve plug has a stem and passage means for admitting live air continuously from the inlet end of the fitting to the space behind the plug, and the plug has an annular metering portion coaxial with, and slightly less in diameter than, the portion of the bore in which the plug is reciprocable.

5. The structure according to claim 1 wherein the tappet includes a stem extending into the power cylinder bore and a spool on the outer end of the stem;

the body has an exhaust duct with an inlet port positioned so that it is closed by the spool when the tappet is in a retracted position and is uncovered by the spool when the tappet is in an extended position;

said stem has passage means continually connected to the power cylinder bore at the end of the power cylinder bore adjacent to the tappet; and

said passage means have an outlet open for communication with said exhaust duct while the tappet is in said extended position and closed while the tappet is in said retracted position.

6. The structure according to claim 1 wherein the means drivingly connecting the valve and tappet is a rigid rod having axially spaced abutments thereon and being incompressible between said abutments;

said rod is free floating relative to the tappet and valve;

said valve includes a plug;

one of said abutments has an end face abuttable with a complementary abutment surface on said plug and the other of said abutments has a face abuttable with a complementary abutment surface on the tappet; and

the distance between said faces closely approximating, but being slightly less than, the distance between the complementary abutment surfaces when the plug is seated and the tappet is fully extended.

7. In a reciprocating air hammer:

a moil member;

a moil driving tappet member;

a body supporting the members for reciprocation to extended and retracted positions, respectively;

a power cylinder bore coaxial with the tappet membet;

a power piston in the bore cylinder reciprocable relative to the body and to the tappet member from a retraCted starting position to an extended position wherein it delivers a blow on the tappet member, and from the extended position to the starting position;

valve means for successively alternately connecting the bore at one face of the power piston to said inlet for admitting air under pressure for driving the power piston on its power stroke, and at the opposite face of the power piston for driving the power piston on its return stroke;

characterized in that:

said body has a live air inlet bore coaxial with, and

connected to, the power cylinder bore;

a cut-off valve plug is movable in the inlet bore to open and seated positions, respectively;

a rigid rod, having axially spaced abutments thereon and being incompressible axially between said abutments, is mounted for free floating movement axially relative to said power cylinder bore;

said abutments have abuttable faces facing away from each other endwise of the rod and abuttable, respectively, with complementary abutment surfaces on the plug and tappet, respectively;

the distance between said faces closely approximating, but slightly less than, the distance between said surfaces when the plug is seated and the tappet is fully extended.

8. The structure according to claim 7 wherein the body has an exhaust valve with an exhaust port; a valving spool on the tappetis reciprocable therein upon reciprocation of the tappet and is positioned relative to the exhaust port to close the port when the tappet is ex tended and to open the port when the tappet is retracted. i

9. The structure according to claim 7 wherein the effective area of the plug, at its inlet face, is such that, when seated and subjected to live air, the plug yieldably holds the tappet and moil in fully extended position.

10. The structure according to claim 7 wherein the rod is stainless steel. iiimfi aanezaaidiag iauaimfimeran the effective area of the plug, at its inlet face, is suf- 10 ficently greater than the effective area at its outlet face so that, while unseated and subjected to live air, the plug yieldably moves the tappet member and moil member to fully extended position against forces urging the tappet member and moil member toward retracted positions, other than forces of predetermined intensity applied directly by the work to the moil member for driving the moil member toward retracted positions.

12. The structure according to claim 11 wherein the cut-off valve is also a metering valve which, when open, meters the flow of air to the valve means. 

1. In a reciprocating air hammer: a moil member; a moil driving tappet member; a body supporting the members for reciprocation to extended and retracted positions, respectively; a power cylinder bore coaxial with the tappet member; a power piston in the bore cylinder reciprocable relative to the body and to the tappet member from a retracted starting position to an extended position wherein it delivers a blow on the tappet member, and from the extended position to the starting position; said body having a live air inlet connected with said bore; valve means for successively alternately connecting the bore at one face of the power piston to said inlet for admitting air under pressure for driving the power Piston on its power stroke, and at the opposite face of the power piston for driving the power piston on its return stroke; characterized in that: a metering cut-off valve is connected to the body inlet and is connectable to a source of air pressurized to a predetermined pressure, and is operative in all open positions, to meter the live air admitted to the power cylinder bore by way of the inlet and valve means, in all open positions of the metering valve, to a rate of flow substantially less than that at which the piston would operate if connected to said source for free and unrestricted flow of the pressurized air to said valve means, and for stopping the admission of air to the power cylinder bore while the valve is closed; and means drivingly connect the valve and tappet for opening and closing the valve in fixed relation to the tappet positions.
 2. The structure according to claim 1 wherein the metering valve includes a valving bore connected to said inlet, and a metering and cut-off valve plug mounted in the valving bore for reciprocation axially thereof, and defining with the valve bore wall a restrictive flow passage operative to restrict the flow through said bore in all open positions of the plug.
 3. The structure according to claim 2 wherein the valve is a separate unit and further includes an inlet fitting, the valving bore is in the fitting, and said fitting, with the valve plug installed therein, is connectable as a subassembly unit to the body.
 4. The structure according to claim 3 wherein the valve plug has a stem and passage means for admitting live air continuously from the inlet end of the fitting to the space behind the plug, and the plug has an annular metering portion coaxial with, and slightly less in diameter than, the portion of the bore in which the plug is reciprocable.
 5. The structure according to claim 1 wherein the tappet includes a stem extending into the power cylinder bore and a spool on the outer end of the stem; the body has an exhaust duct with an inlet port positioned so that it is closed by the spool when the tappet is in a retracted position and is uncovered by the spool when the tappet is in an extended position; said stem has passage means continually connected to the power cylinder bore at the end of the power cylinder bore adjacent to the tappet; and said passage means have an outlet open for communication with said exhaust duct while the tappet is in said extended position and closed while the tappet is in said retracted position.
 6. The structure according to claim 1 wherein the means drivingly connecting the valve and tappet is a rigid rod having axially spaced abutments thereon and being incompressible between said abutments; said rod is free floating relative to the tappet and valve; said valve includes a plug; one of said abutments has an end face abuttable with a complementary abutment surface on said plug and the other of said abutments has a face abuttable with a complementary abutment surface on the tappet; and the distance between said faces closely approximating, but being slightly less than, the distance between the complementary abutment surfaces when the plug is seated and the tappet is fully extended.
 7. In a reciprocating air hammer: a moil member; a moil driving tappet member; a body supporting the members for reciprocation to extended and retracted positions, respectively; a power cylinder bore coaxial with the tappet member; a power piston in the bore cylinder reciprocable relative to the body and to the tappet member from a netracted starting position to an extended position wherein it delivers a blow on the tappet member, and from the extended position to the starting position; valve means for successively alternately connecting the bore at one face of the power piston to said inlet for admitting air under pressure for driving the power piston on its power stroke, and at the opposite face of the power piston for driving the power piston on its return stroke; characterized in that: said body has a live air inlet bore coaxial with, and connected to, the power cylinder bore; a cut-off valve plug is movable in the inlet bore to open and seated positions, respectively; a rigid rod, having axially spaced abutments thereon and being incompressible axially between said abutments, is mounted for free floating movement axially relative to said power cylinder bore; said abutments have abuttable faces facing away from each other endwise of the rod and abuttable, respectively, with complementary abutment surfaces on the plug and tappet, respectively; the distance between said faces closely approximating, but slightly less than, the distance between said surfaces when the plug is seated and the tappet is fully extended.
 8. The structure according to claim 7 wherein the body has an exhaust valve with an exhaust port; a valving spool on the tappet is reciprocable therein upon reciprocation of the tappet and is positioned relative to the exhaust port to close the port when the tappet is extended and to open the port when the tappet is retracted.
 9. The structure according to claim 7 wherein the effective area of the plug, at its inlet face, is such that, when seated and subjected to live air, the plug yieldably holds the tappet and moil in fully extended position.
 10. The structure according to claim 7 wherein the rod is stainless steel.
 11. The structure according to claim 7 wherein the effective area of the plug, at its inlet face, is sufficiently greater than the effective area at its outlet face so that, while unseated and subjected to live air, the plug yieldably moves the tappet member and moil member to fully extended position against forces urging the tappet member and moil member toward retracted positions, other than forces of predetermined intensity applied directly by the work to the moil member for driving the moil member toward retracted positions.
 12. The structure according to claim 11 wherein the cut-off valve is also a metering valve which, when open, meters the flow of air to the valve means. 